/* -*- mode: C -*-  */
/* 
   IGraph library.
   Copyright (C) 2010-2012  Gabor Csardi <csardi.gabor@gmail.com>
   334 Harvard st, Cambridge MA, 02139 USA
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 
   02110-1301 USA

*/

#include <igraph.h>
#include <time.h>

#define DIM 10

igraph_bool_t check_ev(const igraph_matrix_t *A, 
		       const igraph_vector_t *values,
		       const igraph_matrix_t *vectors, igraph_real_t tol) {
  igraph_vector_t v, y;
  int i, j;
  int m=igraph_matrix_ncol(vectors);
  int n=igraph_matrix_nrow(A);
  
  if (igraph_matrix_ncol(A) != n)       { return 1; }
  if (igraph_vector_size(values) != m)  { return 1; }
  if (igraph_matrix_nrow(vectors) != n) { return 1; }

  igraph_vector_init(&y, n);

  for (i=0; i<m; i++) {
    igraph_vector_view(&v, &MATRIX(*vectors, 0, i), n);
    igraph_vector_update(&y, &v);
    igraph_blas_dgemv(/*transpose=*/ 0, /*alpha=*/ 1.0, A, &v, 
		      /*beta=*/ -VECTOR(*values)[i], &y);
    for (j=0; j<n; j++) {
      if (fabs(VECTOR(y)[i]) > tol) {
	printf("Matrix:\n"); igraph_matrix_print(A);
	printf("lambda= %g\n", VECTOR(*values)[i]);
	printf("v= "); igraph_vector_print(&v);
	printf("residual: "); igraph_vector_print(&y);
	return 1; 
      }
    }
  }
  
  igraph_vector_destroy(&y);
  return 0;
}

int main() {

  igraph_matrix_t A;
  igraph_matrix_t vectors, vectors2;
  igraph_vector_t values, values2;
  int i, j;
  int il, iu;
  igraph_real_t vl, vu;
  
  igraph_rng_seed(igraph_rng_default(), 42);
  
  igraph_matrix_init(&A, DIM, DIM);
  igraph_matrix_init(&vectors, 0, 0);
  igraph_vector_init(&values, 0);

  /* All eigenvalues and eigenvectors */

  for (i=0; i<DIM; i++) {
    for (j=i; j<DIM; j++) {
      MATRIX(A, i, j) = MATRIX(A, j, i) = 
	igraph_rng_get_integer(igraph_rng_default(), 1, 10);
    }
  }
  
  igraph_lapack_dsyevr(&A, IGRAPH_LAPACK_DSYEV_ALL, /*vl=*/ 0, /*vu=*/ 0,
		       /*vestimate=*/ 0, /*il=*/ 0, /*iu=*/ 0, 
		       /*abstol=*/ 1e-10, &values, &vectors, /*support=*/ 0);

  if (igraph_vector_size(&values) != DIM) { return 1; }
  if (igraph_matrix_nrow(&vectors) != DIM || 
      igraph_matrix_ncol(&vectors) != DIM) { return 2; }
  if (check_ev(&A, &values, &vectors, /*tol=*/ 1e-8)) { return 3; }

  /* Only a subset */
  
  igraph_matrix_init(&vectors2, 0, 0);
  igraph_vector_init(&values2, 0);

  il=2; iu=5;
  igraph_lapack_dsyevr(&A, IGRAPH_LAPACK_DSYEV_SELECT, /*vl=*/ 0, /*vu=*/ 0,
		       /*vestimate=*/ 0, /*il=*/ il, /*iu=*/ iu, 
		       /*abstol=*/ 1e-10, &values2, &vectors2, 
		       /*support=*/ 0);
  
  if (igraph_vector_size(&values2) != iu-il+1) { return 4; }
  if (igraph_matrix_nrow(&vectors2) != DIM ||
      igraph_matrix_ncol(&vectors2) != iu-il+1) { return 5; }
  for (i=0; i<iu-il+1; i++) {
    igraph_real_t m1=1.0;

    if (fabs(VECTOR(values)[il+i-1] - VECTOR(values2)[i]) > 1e-8) {
      printf("Full:   "); igraph_vector_print(&values);
      printf("Subset: "); igraph_vector_print(&values2);
      return 6;
    }

    if (MATRIX(vectors, 0, il+i-1) * MATRIX(vectors2, 0, i) < 0) {
      m1=-1.0;
    } else { 
      m1=1.0;
    }

    for (j=0; j<DIM; j++) {
      if (fabs(MATRIX(vectors, j, il+i-1) - 
	       m1 * MATRIX(vectors2, j, i)) > 1e-8) {
	printf("Full:\n"); igraph_matrix_print(&vectors);
	printf("Subset:\n"); igraph_matrix_print(&vectors2);
	return 7;
      }
    }
  }

  igraph_vector_destroy(&values2);
  igraph_matrix_destroy(&vectors2);
  
  /* Subset based on an interval */

  igraph_matrix_init(&vectors2, 0, 0);
  igraph_vector_init(&values2, 0);

  il=2; iu=5;
  vl = (VECTOR(values)[il-1] + VECTOR(values)[il-2]) / 2.0;   
  vu = (VECTOR(values)[iu] + VECTOR(values)[iu-1]) / 2.0;

  igraph_lapack_dsyevr(&A, IGRAPH_LAPACK_DSYEV_INTERVAL, vl, vu, 
		       /*vestimate=*/ iu-il+1, /*il=*/ 0, /*iu=*/ 0, 
		       /*abstol=*/ 1e-10, &values2, &vectors2, 
		       /*support=*/ 0);

  if (igraph_vector_size(&values2) != iu-il+1) { return 4; }
  if (igraph_matrix_nrow(&vectors2) != DIM ||
      igraph_matrix_ncol(&vectors2) != iu-il+1) { return 5; }
  for (i=0; i<iu-il+1; i++) {
    igraph_real_t m1=1.0;

    if (fabs(VECTOR(values)[il+i-1] - VECTOR(values2)[i]) > 1e-8) {
      printf("Full:   "); igraph_vector_print(&values);
      printf("Subset: "); igraph_vector_print(&values2);
      return 6;
    }

    if (MATRIX(vectors, 0, il+i-1) * MATRIX(vectors2, 0, i) < 0) {
      m1=-1.0;
    } else { 
      m1=1.0;
    }

    for (j=0; j<DIM; j++) {
      if (fabs(MATRIX(vectors, j, il+i-1) - 
	       m1 * MATRIX(vectors2, j, i)) > 1e-8) {
	printf("Full:\n"); igraph_matrix_print(&vectors);
	printf("Subset:\n"); igraph_matrix_print(&vectors2);
	return 7;
      }
    }
  }  

  igraph_vector_destroy(&values2);
  igraph_matrix_destroy(&vectors2);

  igraph_vector_destroy(&values);
  igraph_matrix_destroy(&vectors);
  igraph_matrix_destroy(&A);

  return 0;
}

